JP6918311B2 - Metal joints, methods for manufacturing metal joints, semiconductor devices and methods for manufacturing semiconductor devices - Google Patents

Description

The present invention relates to a metal joint, a method for manufacturing a metal joint, a semiconductor device, and a method for manufacturing a semiconductor device.

A power semiconductor module has a structure in which one or more power semiconductor chips are incorporated to form a part or the whole of a conversion connection, and the power semiconductor chip and a laminated substrate or a metal substrate are electrically insulated from each other. It is a power semiconductor device with.

Such a laminated substrate of a power semiconductor module is an insulating substrate provided with a conductive plate such as a copper plate as an electrode pattern. In a conductive plate such as a copper plate on an insulating substrate, the copper (Cu) plate and the copper plate are joined by using solder, a silver (Ag) sintered material, or the like. However, the thermal conductivity of the solder is low, and further, if there are unbonded portions or voids in the solder joint layer, the heat dissipation characteristics are deteriorated. Although the silver sintered material has a high thermal conductivity, like solder, there is a concern that the heat dissipation characteristics may deteriorate due to the presence of voids.

A structure in which thick copper plates are joined is preferable in order to improve heat dissipation characteristics, but since the coefficient of thermal expansion differs between the thick copper plate and the insulating substrate such as a ceramic substrate, the thick copper plate is directly bonded onto the insulating substrate at a high temperature. That is difficult. Therefore, a thin copper plate is joined onto the insulating substrate at a high temperature so that the difference in the coefficient of thermal expansion coefficient becomes small, and then the thin copper plate and the thick copper plate on the insulating substrate are joined. At that time, if a solder, a silver sintered material, or the like is used in the same manner as described above, the bonding strength and the thermal conductivity are lowered due to the presence of unbonded portions and voids. Therefore, in joining a thin copper plate and a thick copper plate on an insulating substrate, direct joining without inserting solder, silver paste, or the like is required. Direct bonding is the bonding by bonding metal atoms to each other without sandwiching anything between the metal plates.

As a method for manufacturing a metal joint, at least one of the joint surfaces is plated with an uneven surface having a ten-point average roughness of 0.15 μm to 5 μm and an average length of roughness curve elements of 1.4 μm to 40 μm. There is a technique for forming by processing (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2015-54329

However, the surface of both the thin copper plate and the thick copper plate on the insulating substrate that has been smoothed by polishing or the like is not flat, and there are loosely winding undulations. FIG. 15 is a cross-sectional view showing a state before joining the metal joint according to the conventional example. In FIG. 15, the first metal portion 31 is a thick copper plate, the second metal portion 32 is a thin copper plate, and the waviness 33 is present on the surfaces of the first metal portion 31 and the second metal portion 32. The height difference h3 of the swell 33 is about several μm, for example, in the range of 0.5 μm to 10 μm.

Here, FIG. 16 is a graph showing the relationship between the surface roughness and the breaking stress. In FIG. 16, the horizontal axis represents the surface roughness Ra, and the unit is nm. The vertical axis represents the breaking stress, and the unit is MPa. Here, the surface roughness Ra is the arithmetic mean roughness (Ra) of the surface. Further, the breaking stress is a pressure at which a shear stress is applied to the material and the material breaks. FIG. 16 shows the result of measuring the breaking stress by directly joining the copper plate and the copper plate.

As shown in FIG. 16, when the surface roughness Ra of the copper plate increases from 12 nm to 300 nm, the breaking stress decreases from 67 MPa to 20 MPa. When the height difference h3 is about several μm, the surface roughness Ra is about 200 nm to 2000 nm, and the breaking stress is 20 MPa or less. In order to obtain a practical bonding strength, a breaking stress larger than 20 MPa is required, and it is presumed that sufficient bonding strength cannot be obtained even if a thin copper plate and a thick copper plate on an insulating substrate are bonded.

FIG. 17 is a cross-sectional view showing the configuration of the metal joint according to the conventional example. FIG. 17 shows the result of joining the first metal portion 31 and the second metal portion 32 of FIG. 15 by applying pressure in the direction of arrow A (see FIG. 15). As shown in FIG. 17, the waviness of the surface of the first metal portion 31 and the waviness of the surface of the second metal portion 32 cause the first metal portion 31 and the second metal portion 32 to be joined only locally. There are many gaps at the interface between the first metal portion 31 and the second metal portion 32, and the area of contact between the first metal portion 31 and the second metal portion 32 is narrowed.

As described above, in the conventional example, for example, at the interface between the first metal portion 31 and the second metal portion 32, the ratio of the gap (hereinafter referred to as the gap ratio) is larger than 50%. The gap ratio is a percentage of the gap ratio per unit area at the interface between the first metal portion 31 and the second metal portion 32. The gap ratio is the area where the first metal portion 31 and the second metal portion 32 are in contact with each other / (the area where the first metal portion 31 and the second metal portion 32 are in contact with each other + the first metal portion 31 and the second metal). It can also be expressed as an area that does not come into contact with the portion 32). Therefore, sufficient joining strength cannot be obtained by joining the first metal portion 31 and the second metal portion 32, and further, the heat dissipation characteristics from the second metal portion 32 to the first metal portion 31 also deteriorate.

The surface is flattened by surface treatment in which a flattening material is laminated on the surfaces of the first metal portion 31 and the second metal portion 32 by plating, sputtering, vapor deposition, etc., or CMP (Chemical Mechanical Polishing) finish. It is possible. In this case, sufficient joining strength may be obtained by joining the first metal portion 31 and the second metal portion 32, but there is a problem that the manufacturing process becomes complicated and costly.

For example, when a thick copper plate is joined to a thin copper plate on an insulating substrate of a semiconductor device, there are undulations on the surface of the thin copper plate and the surface of the thick copper plate, so that there are many gaps between the thin copper plate and the thick copper plate. Therefore, sufficient bonding strength between the copper plates cannot be obtained, and the heat dissipation characteristics of the copper plates also deteriorate.

The present invention provides a metal joint and a method for manufacturing a metal joint capable of improving heat dissipation characteristics by joining metal plates having waviness on the surface with sufficient joining strength in order to solve the above-mentioned problems caused by the prior art. The purpose is. A further object of the present invention is to provide a semiconductor device and a method for manufacturing the semiconductor device, which have improved heat dissipation characteristics by using the metal joint on an insulating substrate.

In order to solve the above-mentioned problems and achieve the object of the present invention, the metal joint according to the present invention has the following features. It is a metal joint body in which a first metal part and a second metal part are joined , and is regularly arranged in both the vertical direction and the horizontal direction of the interface between the first metal part and the second metal part in a top view. The gaps are lined up, and the ratio of the gaps at the interface is 50% or less.

In order to solve the above-mentioned problems and achieve the object of the present invention, the metal joint according to the present invention has the following features. It is a metal joint body in which a first metal portion and a second metal portion are joined, and includes an intermediate metal portion having irregularities on both sides, which is sandwiched between the first metal portion and the second metal portion. Gaps are lined up at the interface between the first metal portion and the intermediate metal portion and the interface between the second metal portion and the intermediate metal portion, and the ratio of the gaps at the interface is 50% or less.

Further, the metal joint according to the present invention is characterized in that, in the above-described invention, the gaps are regularly arranged at the interface.

Further, the metal joint according to the present invention is characterized in that, in the above-described invention, the first metal portion and the second metal portion are made of a metal containing copper, silver, gold or platinum.

In order to solve the above-mentioned problems and achieve the object of the present invention, the metal joint according to the present invention has the following features. The semiconductor device includes a semiconductor element, a laminated substrate provided with an electrode pattern and mounted on the semiconductor element, wiring for electrically connecting the semiconductor element and the electrode pattern, and a metal substrate on which the laminated substrate is mounted. Has. The electrode pattern is a metal joint in which a first metal portion and a second metal portion are joined, and is regular in both the vertical direction and the horizontal direction of the interface between the first metal portion and the second metal portion. The gaps are lined up, and the ratio of the gaps at the interface is 50% or less.

In order to solve the above-mentioned problems and achieve the object of the present invention, the method for producing a metal joint according to the present invention has the following features. First, the first step of forming an uneven shape on one surface of the second metal portion is performed. Next, the surface of the second metal portion on which the concave-convex shape is formed and the surface of the first metal portion where the undulation exists are opposed to each other, and the convex portion of the concave-convex shape is plasticized by heating and pressurizing. By deforming, the second step of joining the first metal portion and the second metal portion is performed.

Further, in the above-described invention, the method for producing a metal joint according to the present invention is the first metal portion and the second metal portion using a reducing gas after the first step and before the second step. It is characterized by including a step of removing the oxide film of the above.

In order to solve the above-mentioned problems and achieve the object of the present invention, the method for producing a metal joint according to the present invention has the following features. First, the first step of forming an uneven shape on both surfaces of the intermediate metal portion is performed. Next, one surface of the first metal portion and one surface of the intermediate metal portion are opposed to each other, and one surface of the second metal portion and the other surface of the intermediate metal portion are opposed to each other, and heated and applied. The second step of joining the first metal portion and the intermediate metal portion, and the second metal portion and the intermediate metal portion is performed by plastically deforming the convex portion of the concave-convex shape by pressure.

Further, in the above-described invention, the method for producing a metal joint according to the present invention is a method for producing the first metal portion and the second metal portion by using a reducing gas after the first step and before the second step. It is characterized by including a step of removing the oxide film of the intermediate metal portion.

Further, the method for producing a metal joint according to the present invention is characterized in that, in the above-mentioned invention, the reducing gas contains formic acid or hydrogen.

Further, the method for producing a metal joint according to the present invention is characterized in that, in the above-described invention, the height of the convex portion of the concave-convex shape is within the range of 0.1 to 20 μm.

Further, the method for producing a metal joint according to the present invention is characterized in that, in the above-described invention, the width of the convex portion of the concave-convex shape is within the range of 1 to 200 μm.

Further, the method for producing a metal joint according to the present invention is characterized in that, in the above-described invention, the distance between the convex portions of the concave-convex shape is within the range of 1 to 200 μm. Further, in the method for manufacturing a metal joint according to the present invention, in the above-described invention, the ratio of the width of the convex portion of the concave-convex shape to the interval of the convex portion of the concave-convex shape is in the range of 0.5 to 4. It is characterized by that. Further, the method for producing a metal joint according to the present invention is characterized in that, in the above-described invention, the height difference of the waviness is within the range of 0.5 μm to 10 μm.

In order to solve the above-mentioned problems and achieve the object of the present invention, the method for manufacturing a semiconductor device according to the present invention has the following features. First, the first step of forming an uneven shape on one surface of the second metal portion is performed. Next, the surface of the second metal portion on which the uneven shape is formed and the surface of the first metal portion provided on the laminated substrate in which waviness exists are made to face each other, and the surface is heated and pressurized. A second step of forming an electrode pattern is performed by joining the first metal portion and the second metal portion by plastically deforming the convex portion of the concave-convex shape. Next, a third step of mounting the semiconductor element on the laminated substrate is performed. Next, a fourth step of assembling the laminated substrate into the laminated assembly is performed. Next, a fifth step of electrically connecting the semiconductor element and the electrode pattern on the laminated substrate is performed. Next, a sixth step of combining the resin case with the laminated assembly is performed.

According to the invention described above, the first metal portion or the second metal portion is provided with an uneven shape. By plastically deforming this uneven shape by pressurization and heating, the contact area between the first metal portion and the second metal portion can be increased, and the joint strength can be improved. Further, the convex portion having an uneven shape is plastically deformed and enters the concave portion of the waviness on the surface, and the convex portion fills the gap. As a result, the ratio of gaps is smaller than before, heat dissipation characteristics are improved, and high heat resistance is obtained.

Further, the first metal part and the second metal part are heated and pressurized in a formic acid environment. For this reason, metal atoms without an oxide film are exposed in the contact portion, and the metal atoms are directly bonded to each other, so that the bonding strength is high and the heat dissipation characteristics are also improved. Further, since a low melting point material such as solder is not used for the contact portion, the metal joint does not remelt, so that a highly heat-resistant metal joint can be realized.

According to the semiconductor device of the above-described invention, a thick copper plate can be formed by joining a thick copper plate having a concavo-convex shape to a thin copper plate on an insulating substrate. As a result, the heat dissipation characteristics of power semiconductor modules can be achieved by surface treatment such as plating, sputtering, and vapor deposition of thin and thick copper plates on an insulating substrate, and by an inexpensive manufacturing process that does not require an intermediate metal layer such as solder or silver sintered material. Can be improved.

According to the metal joint and the method for producing a metal joint according to the present invention, it is possible to bond metal plates having waviness on the surface with sufficient joint strength and to improve heat dissipation characteristics. Further, according to the semiconductor device and the method for manufacturing the semiconductor device according to the present invention, there is an effect that the heat dissipation characteristics can be improved by using the metal joint on the insulating substrate.

It is sectional drawing which shows the structure of the metal joint body which concerns on Embodiment 1. FIG. FIG. 5 is an enlarged view of a joint portion A of FIG. 1 of the metal joint according to the first embodiment. It is sectional drawing which shows the state in the process of manufacturing the metal joint which concerns on Embodiment 1 (the 1). FIG. 2 is a cross-sectional view showing a state in which the metal joint according to the first embodiment is in the process of being manufactured (No. 2). FIG. 3 is a cross-sectional view showing a state in which the metal joint according to the first embodiment is in the process of being manufactured (No. 3). It is sectional drawing which shows the state in the process of manufacturing the metal joint which concerns on Embodiment 1 (the 4). FIG. 5 is an enlarged view of a portion B of FIG. 5 in a state in which the metal joint according to the first embodiment is being manufactured. It is a top view which shows the detail of the perforated plate in FIG. It is sectional drawing which shows the structure of the power semiconductor module using the metal joint which concerns on Embodiment 1. FIG. It is sectional drawing which shows the structure of the metal joint body which concerns on Embodiment 2. It is sectional drawing which shows the state in the process of manufacturing of the metal joint body which concerns on Embodiment 2. FIG. It is a top view which shows typically the observation result of the joint part of the metal joint which concerns on Example. It is a top view which shows typically the observation result of the joint part of the metal joint which concerns on the prior art. It is a table which shows the relationship between the width, height, and spacing of the convex part of the joint part of the metal joint body which concerns on Example, and the joint strength and the gap ratio. It is sectional drawing which shows the state before joining of the metal joint body which concerns on a prior art example. It is a graph which shows the relationship between the surface roughness and the breaking stress. It is sectional drawing which shows the structure of the metal joint body which concerns on the prior art example.

Hereinafter, preferred embodiments of the metal joint, the method for manufacturing the metal joint, the semiconductor device, and the method for manufacturing the semiconductor device according to the present invention will be described in detail with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing the configuration of the metal joint according to the first embodiment. As shown in FIG. 1, the metal joint is composed of a first metal portion 1 and a second metal portion 2 that are directly joined. The first metal portion 1 is, for example, a thin copper plate on an insulating substrate, and the second metal portion 2 is a thick copper plate directly bonded to the thin copper plate. Since the metal joint body joins the first metal portion 1 and the second metal portion 2 having the waviness 33 on the surface, the gap 11 is formed on the contact surface between the first metal portion 1 and the second metal portion 2. Exists.

However, in the first embodiment, the gaps 11 are regularly provided. In the first embodiment, as will be described in detail later, the surface of the second metal portion 2 is provided with an uneven shape. The surface of the first metal portion 1 may be provided with an uneven shape. A gap 11 is formed by this uneven shape.

Here, FIG. 2 is an enlarged view of the joint portion A of FIG. 1 of the metal joint according to the first embodiment. As shown in FIG. 2, since the uneven shape is formed so that the pitch of the unevenness (distance w1 between the convex portions) is narrower than that of the waviness 33, the uneven shape enters the concave portion of the waviness 33 on the surface, and the convex portion is formed. The gap due to the swell 33 is filled. As a result, the metal joint has few unbonded portions and voids, and the gap ratio (ratio of gaps) on the contact surface between the first metal portion 1 and the second metal portion 2 is smaller than that in the conventional example. Specifically, in the first embodiment, the gap ratio is 50% or less. Therefore, the heat dissipation characteristics are improved and the heat resistance is high. The gap ratio will be described later.

Further, the convex portion having the concave-convex shape is plastically deformed by the pressure applied at the time of joining to form the first metal portion 1, the second metal portion 2, and the contact portion 12. As shown in FIG. 2, the tip of the convex portion is crushed, and the tip of the convex portion comes into contact with the swell 33. With this contact portion 12, the area in which the first metal portion 1 and the second metal portion 2 are in contact (hereinafter referred to as the contact area) can be increased. Therefore, in the first embodiment, the contact area of the contact portion 12 can be increased and the bonding strength is improved as compared with the case where the wavy surfaces are directly bonded to each other as in the conventional example. Therefore, the gap ratio is more preferably 50% or less. This is because if it is less than this, the bonding strength becomes 20 MPa or more. Further, for example, a regular gap 11 is formed at the joint portion corresponding to the uneven shape having a regular uneven pitch provided on the surface of the second metal portion 2. That is, the gap 11 is regularly formed at a pitch corresponding to the pitch of a predetermined uneven shape provided on the surface of the second metal portion 2 or the like. However, some of the convex portions may be deformed to narrow or eliminate the gap 11. In fact, the joint portion where sufficient joint strength is obtained has a regular gap of 60% or more.

Further, as will be described later, the contact surface between the first metal portion 1 and the second metal portion 2 is heated and pressurized in _{a reducing gas, for example, formic acid (CH 2} O _{2) environment.} Therefore, in the contact portion 12, metal atoms without an oxide film are exposed, and the metal atoms are directly bonded to each other, so that the bonding strength is high and the heat dissipation characteristics are also improved. Therefore, the final clearance ratio is more preferably 5% or more so that the reducing gas reaches the details of the bonding interface.

Further, the gap 11 due to the concave-convex-shaped recess becomes a vacancy that communicates with the outside, and the reducing gas reaches the entire interface between the first metal portion 1 and the second metal portion 2, the reducing property by the reducing gas is improved, and oxidation is performed. Since the film is reduced, the bonding strength is improved.

Further, the metal of the first metal portion 1 and the second metal portion 2 is preferably not very hard because it is plastically deformed by heating and pressure. Further, when an oxide film is formed, metal atoms cannot be directly bonded to each other, and the bonding strength and heat dissipation characteristics deteriorate. Therefore, it is preferable that the metal is difficult to form an oxide film. Further, when atoms are directly bonded to each other, if the atoms enter each other, the bonding strength and heat dissipation characteristics are improved. Therefore, it is preferable that the metal is a metal in which the atoms are easily diffused into each other. Therefore, it is preferable that the metal of the first metal portion 1 and the second metal portion 2 is the same metal. Specifically, the first metal portion 1 and the second metal portion 2 are preferably metals containing copper, silver (Ag), gold (Au) or platinum (Pt). Further, it is more preferable that the first metal portion 1 and the second metal portion 2 are copper. In the case of copper, copper is the main component, and 80 wt% or more is preferable. Within this range, it has the same effect as that of pure copper. Also, silver, gold, and platinum are similar to copper. In the following, the copper plate will be described, but the present invention is not limited to this.

Further, in the first embodiment, the first metal part 1 and the second metal part 2 are joined to each other, but more than two metal parts may be joined. The thickness of the metal portion can be increased by increasing the number of layers on which the metal portion is laminated.

(Method for manufacturing a metal joint according to the first embodiment)
Next, a method for manufacturing the metal joint according to the first embodiment will be described. 3 to 6 are cross-sectional views showing a state in which the metal joint according to the first embodiment is in the process of being manufactured. First, a perforated plate 4 made of SUS (Stainless Steel) having a film thickness of h1 in which holes 13 having a diameter w11 are regularly arranged and a second metal portion 2 are prepared. FIG. 8 is a top view showing the details of the perforated plate in FIG. In the perforated plate 4, for example, the holes 13 are provided so that the opening ratio is about 50%. The state up to this point is shown in FIG.

Next, by pressing the perforated plate 4 onto the second metal portion 2, an uneven shape is formed on the surface of the second metal portion 2. Since the concave-convex-shaped convex portion 14 is formed from the circular hole 13 having a diameter w11, the diameter w21 of the columnar convex portion 14 is about the same as the diameter w11 of the hole 13, and the height h2 of the convex portion 14 Is about the same as the film thickness h1 of the perforated plate 4. Further, since the convex portion 14 formed by the press has a rounded corner, the central portion first contacts the first metal portion 1, and plastic deformation is likely to occur, so that the contact area increases. The convex portion may be a pillar, or may be a prism such as a square pillar, and the shape of the bottom surface may be a polygon such as a square or an ellipse. Further, the convex portion is preferably formed perpendicular to the plane of the plate-shaped metal portion, but may be inclined like an oblique prism.

Here, the height h2 of the convex portion 14 having the concave-convex shape is preferably a height sufficient to enter the concave portion (see FIG. 1) of the waviness 33 on the surface. If the height h2 is too large, the proportion of the gap 11 increases, so that the thermal conductivity decreases and the bonding strength deteriorates. Therefore, for example, the height h2 of the convex portion 14 having a concave-convex shape is preferably in the range of 0.1 to 20 μm.

Further, the smaller the width w21 of the convex portion 14 of the concave-convex shape is, the easier it is to be plastically deformed, and the smaller the distance w22 of the convex portion 14 of the concave-convex shape is, the more the number of convex portions 14 is and the larger the contact area is, which is preferable. Therefore, for example, it is preferable that the width w21 of the convex portion 14 having the concave-convex shape and the distance w22 between the convex portions having the concave-convex shape are both within the range of 1 to 200 μm. Further, the convex portion 14 and the concave portion 15 may be formed in the second metal portion 2 by etching instead of pressing. The state up to this point is shown in FIG. The swell may remain on the surface of the second metal portion 2.

Next, a state in which a second metal portion 2 to be joined to the first metal portion 1 is prepared and a gap is opened between the first metal portion 1 and the second metal portion 2 in a jig capable of applying pressure. Place with. The state up to this point is shown in FIG. FIG. 5 relates to a laminated substrate of a semiconductor device, but the same applies to the joining of the first metal portion and the second metal portion. In the laminated substrate of the semiconductor device, the first metal portion 1 is provided on both sides of the insulating substrate 5, but it may be the case of only one side. Here, FIG. 7 is an enlarged view of a portion B of FIG. 5 in a state in which the metal joint according to the first embodiment is being manufactured. As shown in FIG. 7, a waviness 33 exists on the surface of the first metal portion 1, and pressure is applied in the direction of arrow A.

Next, a reducing gas (gas) such as formic acid or hydrogen (H ₂ ) is introduced into the gap to remove the oxide film on the surfaces of the first metal portion 1 and the second metal portion 2 to create a new surface. The atmospheric pressure (gas pressure) at this time may be an atmospheric pressure or a reduced pressure environment. Next, the first metal part 1 and the second metal part 2 are joined to each other by pressurizing and heating the first metal part 1 and the second metal part 2. For heating, for example, the temperature of the first metal portion 1 and the second metal portion 2 is set to about 150 ° C. to 300 ° C. by a heater. As the pressure, for example, a pressure of 10 MPa to 50 MPa is applied so as to locally exceed the plastic deformation pressure of copper. The state up to this point is shown in FIG. As described above, the metal joint shown in FIG. 1 is manufactured. The thickness of the first metal portion 1 may be thicker than or equal to the thickness of the second metal portion 2. The conductive plates are joined to each other to form a thick conductive plate as an electrode pattern. Further, the uneven shape may be formed on the first metal portion 1 instead of the second metal portion 2, or the uneven shape may be formed on both of them.

As described above, according to the first embodiment, the first metal portion or the second metal portion is provided with an uneven shape. By plastically deforming this uneven shape by pressurization and heating, the contact area between the first metal portion and the second metal portion can be increased, and the joint strength can be improved. Further, the convex portion having an uneven shape is plastically deformed and enters the concave portion of the waviness on the surface, and the convex portion fills the gap. As a result, the ratio of gaps is smaller than before, heat dissipation characteristics are improved, and high heat resistance is obtained.

Further, the first metal part and the second metal part are heated in a reducing gas atmosphere environment such as formic acid, and are pressurized while being heated. When pressurizing, the atmosphere does not have to be a reducing gas atmosphere. For this reason, metal atoms without an oxide film are exposed in the contact portion, and the metal atoms are directly bonded to each other, so that the bonding strength is high and the heat dissipation characteristics are also improved. Further, since a low melting point material such as solder is not used for the contact portion, the metal joint does not remelt, so that a highly heat-resistant metal joint can be realized.

(Semiconductor Device of Embodiment 1)
FIG. 9 is a cross-sectional view showing the configuration of a power semiconductor module using the metal joint according to the first embodiment. As shown in FIG. 9, the power semiconductor module includes a power semiconductor chip 21, an insulating substrate 22, an electrode pattern 23, a metal substrate 24, a terminal case 25, a metal terminal 26, a metal wire 27, and a lid 28. And a sealing material 29.

The power semiconductor chip 21 is a power semiconductor chip such as an IGBT (Insulated Gate Bipolar Transistor) or a diode, and is mounted on an insulating substrate 22. A substrate provided with an electrode pattern 23 such as copper on the front surface and the back surface of an insulating substrate 22 such as a ceramic substrate is referred to as a laminated substrate. The laminated substrate is solder-bonded to the metal substrate 24. The terminal case 25 is adhered to the metal substrate 24 with an adhesive. The terminal case 25 is made of a thermoplastic resin such as polyphenylene sulfide (PPS), and is insert-molded to fix the metal terminal 26 that takes out a signal to the outside. The metal terminal 26 is fixed on the laminated substrate by soldering, penetrates the lid 28, and protrudes to the outside. The metal wire 27 electrically connects the power semiconductor chip 21 and the metal terminal 26. The lid 28 is made of the same thermoplastic resin as the terminal case 25. The sealing material 29 is filled in the terminal case 25 as a sealing resin that insulates and protects the power semiconductor chip 21 on the surface of the laminated substrate and on the substrate on which the power chip is mounted.

In the semiconductor device of the first embodiment, it is preferable that the electrode pattern 23 on the front surface of the insulating substrate 22 is composed of the metal joint of the first embodiment. By thickening the electrode pattern 23 on the front surface, the heat of the power semiconductor chip 21 can be diffused. As described above, the electrode pattern 23 on the front surface is a directly bonded thin metal plate and a thick metal plate, and has the same effect as the metal bonded body of the first embodiment. For example, in the semiconductor device of the first embodiment, the gap ratio at the interface between the thin metal plate and the thick metal plate of the electrode pattern 23 on the front surface is 50% or less. As a result, the heat dissipation characteristics of the semiconductor device of the first embodiment are improved, and the semiconductor device has high heat resistance.

Further, in the semiconductor device of the first embodiment, it is preferable that the electrode pattern 23 on the back surface of the insulating substrate 22 is composed of the metal joint of the first embodiment. Further, by making the thickness of the electrode patterns 23 on the front surface and the back surface the same, the warp of the insulating substrate 22 can be eliminated. Further, in the semiconductor device of the first embodiment, the joint body of the electrode pattern 23 and the metal substrate 24 can also be composed of the metal joint body of the first embodiment. As described above, the electrode pattern 23 is formed by directly joining the first metal portion 1 and the second metal portion 2, but the thickness of the first metal portion 1 is larger than the thickness of the second metal portion 2. It can be thick or equivalent.

(Manufacturing method of semiconductor device according to the first embodiment)
Next, a method of manufacturing the semiconductor device according to the first embodiment will be described. First, a thin copper plate (first metal portion) is joined to the insulating substrate 22 at a high temperature. Next, for example, an uneven shape is formed on one surface of a thick copper plate (second metal portion) by the same method as the method for manufacturing a metal joint according to the first embodiment. Next, the surface of the thick copper plate having the uneven shape and the surface of the thin copper plate are opposed to each other, and the surface of the thin copper plate is placed on a jig capable of applying pressure with a gap between the thin copper plate and the thick copper plate. The copper plate on which the above-mentioned unevenness is formed may be thinner or equivalent to the copper plate on the insulating substrate. The action of direct bonding is the same.

Next, a reducing gas such as formic acid or hydrogen is introduced into the gap to remove the oxide film on the surface of the thin copper plate and the thick copper plate to create a new surface. Next, the thin copper plate and the thick copper plate are joined by pressurizing and heating. By this joining, the electrode pattern 23 is formed on the insulating substrate 22.

Next, the power semiconductor chip 21 is mounted on the insulating substrate 22 by joining the power semiconductor chip 21 to the electrode pattern 23 on the insulating substrate 22 using a bonding material such as solder. Next, the power semiconductor chip 21 and the electrode pattern 23 on the insulating substrate 22 are electrically connected by the metal wire 27. Next, the metal terminal 26 is attached to the electrode pattern 23 to which the metal wire 27 is connected. Next, using a bonding material such as solder, these are bonded to the metal substrate 24 to assemble a laminated assembly composed of a power semiconductor chip 21, an insulating substrate 22, and a metal substrate 24. Further, instead of the metal wire 27, a metal terminal may be joined.

Next, the terminal case 25 is adhered to this laminated assembly. Next, the terminal case 25 is filled with a sealing material 29 such as a hard resin such as an epoxy resin. After that, heat treatment is performed under predetermined conditions to cure the mixture. Next, a lid 28 is attached to prevent the sealing material 29 from leaking to the outside. As described above, the power semiconductor module according to the first embodiment of the present invention can be manufactured.

As described above, according to the semiconductor device of the first embodiment, a thick copper plate can be formed by joining a thick copper plate having a concave-convex shape to a thin copper plate on an insulating substrate. As a result, the heat dissipation characteristics of power semiconductor modules can be achieved by surface treatment such as plating, sputtering, and vapor deposition of thin and thick copper plates on an insulating substrate, and by an inexpensive manufacturing process that does not require an intermediate metal layer such as solder or silver sintered material. Can be improved.

(Embodiment 2)
FIG. 10 is a cross-sectional view showing the configuration of the metal joint according to the second embodiment. As shown in FIG. 10, the metal joint is composed of a directly bonded first metal portion 1, an intermediate metal layer 3, and a second metal portion 2. The first metal portion 1 is, for example, a thin copper plate on an insulating substrate, and the second metal portion 2 is a thick copper plate. The intermediate metal layer 3 is a thin copper plate. In the metal joint, the first metal portion 1 having the waviness 33 on the surface and the intermediate metal layer 3 and the intermediate metal layer 3 and the second metal portion 2 having the waviness 33 on the surface are joined to each other. 1 There is a gap 11 at the contact surface between the metal portion 1 and the intermediate metal layer 3 and the intermediate metal layer 3 and the second metal portion 2.

However, in the second embodiment, the gaps 11 are regularly provided as in the first embodiment. Concavo-convex shapes are provided on both surfaces of the intermediate metal layer 3. A gap 11 is formed by this uneven shape.

By making the concave-convex shape of the second embodiment the same shape as that of the first embodiment, the contact surface between the first metal portion 1 and the intermediate metal layer 3 and the contact between the intermediate metal layer 3 and the second metal portion 2 The ratio of the gap 11 on the surface can be made smaller than in the case of the conventional example. Specifically, as in the first embodiment, the gap ratio is 50% or less. Therefore, the heat dissipation characteristics are improved and the heat resistance is high. The thickness of the first metal portion 1 may be thicker than or equal to the thickness of the second metal portion 2.

Further, the uneven shape is deformed by the pressure applied at the time of joining to form a contact portion 12 between the first metal portion 1 and the intermediate metal layer 3 and a contact portion 12 between the intermediate metal layer 3 and the second metal portion 2. .. With the contact portion 12, the area where the first metal portion 1 and the intermediate metal layer 3 are in contact with each other and the area where the intermediate metal layer 3 and the second metal portion 2 are in contact with each other (hereinafter, contact area) are the same as in the first embodiment. ) Can be increased and the bonding strength is improved.

Further, in the second embodiment as in the first embodiment, the contact surface between the first metal portion 1 and the intermediate metal layer 3 and the contact surface between the intermediate metal layer 3 and the second metal portion 2 are under a formic acid environment. It is heated and pressurized in the above manner, and has high bonding strength and improved heat dissipation characteristics as in the first embodiment.

Further, the height of the uneven gap 11 of the intermediate metal layer 3, the width of the gap, and the gap between the gaps are the same as those in the first embodiment, and the first metal portion 1, the second metal portion 2, and the intermediate are the same. The metal layer 3 is the same metal as in the first embodiment. The thickness of the intermediate metal layer 3 is preferably 0.1 mm to 2 mm. This is because, in this range, the intermediate metal layer 3 itself is deformed and easily follows the shape (waviness, warp, etc.) of the joint surfaces of the first metal portion 1 and the second metal portion 2.

The same metal as the material of the first embodiment can be used for the first metal portion 1, the second metal portion 2, and the intermediate metal layer 3. Specifically, it is preferably a metal containing copper, silver, gold or platinum. The metals of the first metal portion 1, the second metal portion 2, and the intermediate metal layer 3 are preferably the same metal. Further, it is more preferable that the first metal portion 1 and the second metal portion 2 are made of copper.

Further, in the second embodiment, the intermediate metal layer 3 is joined between the first metal portion 1 and the second metal portion 2, but more than two metal portions may be joined. In this case, it is not necessary to provide the intermediate metal layer 3 between all the metal portions. For example, when joining three metal parts, it may be a metal part-metal part-intermediate metal layer-metal part.

(Method for manufacturing a metal joint according to the second embodiment)
Next, a method for manufacturing the metal joint according to the second embodiment will be described. FIG. 11 is a cross-sectional view showing a state in which the metal joint according to the second embodiment is in the process of being manufactured. First, the same perforated plate 4 as in the first embodiment and the intermediate metal layer 3 are prepared.

Next, by pressing the perforated plate 4 onto the intermediate metal layer 3, the convex portion 14 and the concave portion 15 are formed on the surface of the intermediate metal layer 3. At this time, the convex portion 14 and the concave portion 15 are formed on both surfaces of the intermediate metal layer 3, but they may be formed at the same time or separately. The shape of the convex portion 14 may be the same as that of the first embodiment. It is preferable that at least a part of the convex portion 14 on one side of the intermediate metal layer 3 is provided so as to face the convex portion 14 on the other surface. This is because if the convex portions 14 are formed alternately, it is difficult for the pressure to be uniformly transmitted.

Next, the first metal part 1 and the second metal part 2 are prepared, and a jig capable of applying pressure is used between the first metal part 1 and the intermediate metal layer 3 and between the intermediate metal layer 3 and the second metal layer 3. It is arranged with a gap between it and the metal portion 2. This state is shown in FIG.

Next, a reducing gas such as formic acid or hydrogen is introduced into the gap to remove the oxide film on the surface of the first metal portion 1, the second metal portion 2 and the intermediate metal layer 3, and a new surface is produced. Next, the first metal portion 1, the second metal portion 2 and the intermediate metal layer 3 are joined by pressurizing and heating. Here, the conditions of pressurization and heating may be the same as those of the first embodiment. As described above, the metal joint shown in FIG. 10 is manufactured.

As described above, according to the second embodiment, the intermediate metal layer is provided with an uneven shape. By plastically deforming this uneven shape by pressurization and heating, the contact area of the contact portion can be increased and the joint strength can be improved. Further, the convex portion having an uneven shape is plastically deformed and enters the concave portion of the waviness on the surface, and the convex portion fills the gap. As a result, the ratio of gaps is smaller than before, heat dissipation characteristics are improved, and high heat resistance is obtained. Further, in the second embodiment, since the intermediate metal layer can follow the warp of the first metal portion and the second metal portion, it is particularly effective when the warp is large.

Further, the first metal portion, the second metal portion and the intermediate metal layer are heated and pressurized in a formic acid environment. For this reason, metal atoms without an oxide film are exposed in the contact portion, and the metal atoms are directly bonded to each other, so that the bonding strength is high and the heat dissipation characteristics are also improved.

The semiconductor device of the second embodiment is the same as the first embodiment except that the electrode pattern 23 is the metal joint according to the second embodiment, and thus the description thereof will be omitted. Further, in the method for manufacturing the semiconductor device of the second embodiment, the other manufacturing steps are the same as that of the first embodiment, except that the manufacturing method of the electrode pattern 23 is the manufacturing method of the metal joint according to the second embodiment. Since it is the same as the above, the description thereof will be omitted.

(Example)
Hereinafter, examples will be described. In the example, a SUS perforated plate 4 having a film thickness of 100 μm and a second metal portion 2 having a film thickness of 1 mm, in which holes 13 having a diameter of 100 μm are lined up with an aperture ratio of 50%, were prepared. By pressing the perforated plate 4 onto the second metal portion 2, a convex portion 14 and a concave portion 15 having a height of 15 μm were formed on the surface of the second metal portion 2.

After that, in the example, formic acid was introduced and treated at a temperature of 280 ° C. for 30 minutes to remove the surface oxide film. After that, the first metal portion 1 and the second metal portion 2 were joined by applying a pressure of 15 kN at a temperature of 280 ° C. Here, FIG. 12 is a top view schematically showing the observation result of the joint portion of the metal joint according to the embodiment. FIG. 13 is a top view schematically showing the observation result of the joint portion of the metal joint according to the conventional example.

FIG. 12 is an image of a joint portion between the first metal portion 1 and the second metal portion 2 observed with a SAT (Scanning Acoustic Tomography: ultrasonic flaw detector) having a gap of 0.5 μm or more. Further, FIG. 13 is an image of the joint portion between the first metal portion 31 and the second metal portion 32 of the conventional example observed by SAT for comparison. In FIGS. 12 and 13, the black portion is the portion where the first metal portion and the second metal portion are in contact with each other, and the white portion is a portion where they are not in contact with each other. In the case of the embodiment of FIG. 12, not only the convex portion of the black dot but also the periphery thereof is in contact, and the white portion that is not in contact is reduced. On the other hand, in the case of the conventional example of FIG. 13, the area of the white portion that is not in contact is large, and in FIG. 13, there are two white portions 16 having a large area. Therefore, in the embodiment, the first metal portion 31 and the second metal portion 32 are satisfactorily bonded, the bonding strength is high, and the heat dissipation characteristics are also good. On the other hand, in the conventional example, it can be seen that the first metal portion 31 and the second metal portion 32 are not sufficiently bonded, the bonding strength is low, and the heat dissipation characteristics are also poor. The gap ratio (ratio of gaps) is the ratio of the area of the non-contact portion (gap of 0.5 μm or more) in the joint portion, and is obtained from the image observed by the SAT. The image of SAT is an observation of the joint surface from above. Further, the average of observing 10 points of 1 mm square was taken as the gap ratio.

FIG. 14 is a table showing the relationship between the width (diameter), height, and spacing of the columnar convex portion of the joint portion of the metal joint according to the embodiment and the joint strength and gap ratio. In FIG. 14, W is the width (diameter) of the concave-convex columnar convex portion, and corresponds to the width w21 of the convex portion 14 in FIG. Further, D is the interval between the convex portions having a concave-convex shape, and corresponds to the interval w22 of the convex portions 14 in FIG. Further, h is the height of the convex portion having a concave-convex shape, and corresponds to the height h2 of the convex portion 14 in FIG. Each unit is μm. The density (W / D) is the ratio of the width W to the interval D, and the larger this value, the smaller the number (density) of the convex portions per unit area.

The joint strength was determined by measuring the strength of the joint portion of the metal joint by a shear strength test, and when it was 20 MPa or more, it was evaluated as ⊚, and when it was 15 to 20 MPa, it was evaluated as ◯. This is because if the joint strength is not 15 MPa or more, cracks or the like may occur at the joint due to the thermal stress when the metal joint is used for the power semiconductor module. The clearance ratio was determined by the above-mentioned SAT evaluation.

In FIG. 14, Examples 1 to 4 are the results of evaluating the bonding strength with W and D as 100 μm and h as 0.1 μm, 1 μm, 10 μm, and 20 μm. In this case, theoretically, the density (W / D) is all 1, and the density of the convex portion is constant. The aspect ratio h / W of the convex portion is 0.001, 0.01, 0.1, 0.2, and the ratio of the convex portion area to the total area is constant. As shown in FIG. 14, in Examples 1 to 4, the joint strengths were all ⊚, the gap ratio was 50% or less, and good joint strength was shown.

Further, in FIG. 14, Examples 5 to 7 are the results of evaluating the bonding strength with D as 100 μm, h as 10 μm, and W as 5 μm, 50 μm, and 200 μm. In this case, the density (W / D) is 0.05, 0.5, 2, and the aspect ratio (aspect ratio) h / W of the convex portion is 2, 0.2, 0.05, which is the total area. The ratio of the area of the convex portion to the relative is 0.2%, 10.1%, and 40.4%. As shown in FIG. 14, the bonding strength was ◯ in Example 5, but the bonding strength was ⊚ in Examples 6 and 7, indicating good bonding strength.

Further, in FIG. 14, Examples 8 to 11 are the results of evaluating the bonding strength with W being 100 μm, h being 10 μm, and D being 5 μm, 25 μm, 50 μm, and 200 μm. In this case, the density (W / D) is 20, 4, 2, 0.5, and the aspect ratio h / W of the convex portion is constant at 0.1, and the convex portion with respect to the entire area. The ratio of the area of is 82.5%, 58%, 40.3%, 10.1%. As shown in FIG. 14, in Example 8, the bonding strength was ◯, but in Examples 9 to 11, the bonding strength became ⊚, indicating good bonding strength. The waviness of the initial surface of the first metal part or the second metal part was evaluated by the average height Wz of the waviness curve element, and the above result was obtained when the Wz was 0.1 to 10 μm. Wz was measured by the method described in JIS-B0601-2001, and the cutoff value λc of the high frequency component cutoff filter was set to 0.25 mm. In the joint portion where good joint strength is obtained, a gap 11 corresponding to the pitch of the predetermined recesses on the surface of the second metal portion 2 is formed, and a rule for the number of the predetermined recesses on the joint surface. The ratio of the number of target gaps 11 (degree of regularization) was 60% or more.

From the above results, it can be seen that, as in Example 5, when the width W is small, the ratio of the area of the convex portion is small and the contact area is small, so that the joint strength is slightly deteriorated. Further, as in Example 8, when the interval D is small, the ratio of the area of the convex portions is large and the gap between the convex portions is small. Therefore, it is estimated that the gap ratio is small but the joint strength is slightly deteriorated. In addition, the semiconductor device using the laminated substrate prepared under the conditions of the above-mentioned Examples showed good results in a reliability test such as a heat cycle test.

As described above, the metal joint, the method for manufacturing the metal joint, and the method for manufacturing the semiconductor device and the semiconductor device according to the present invention are the power conversion device such as an inverter, the power supply device such as various industrial machines, and the igniter of an automobile. It is useful for power semiconductor devices used in such applications.

1 1st metal part 2 2nd metal part 3 Intermediate metal layer 4 Perforated plate 5 Insulated substrate 11 Gap 12 Contact part 13 Hole 14 Convex part 15 Recessed part 16 Large white part 21 Power semiconductor chip 22 Insulated substrate 23 Electrode pattern 24 Metal Board 25 Terminal case 26 Metal terminal 27 Metal wire 28 Lid 29 Encapsulant 31 First metal part 32 Second metal part 33 Waviness

Claims (16)

A metal joint in which a first metal part and a second metal part are joined.
When viewed from above, regular gaps are lined up in both the vertical and horizontal directions of the interface between the first metal portion and the second metal portion, and the ratio of the gaps at the interface is 50% or less. A metal joint characterized by being. A metal joint in which a first metal part and a second metal part are joined.
An intermediate metal portion having irregularities on both sides, which is sandwiched between the first metal portion and the second metal portion, is provided.
Gap is lined up at the interface between the first metal part and the intermediate metal part and the interface between the second metal part and the intermediate metal part, and the ratio of the gap at the interface is 50% or less. A metal joint characterized by. The metal joint according to claim 1 or 2, wherein the gaps are regularly arranged at the interface. The metal joint according to any one of claims 1 to 3, wherein the first metal portion and the second metal portion are made of a metal containing copper, silver, gold or platinum. A semiconductor having a semiconductor element, an electrode pattern, a laminated substrate on which the semiconductor element is mounted, a wiring for electrically connecting the semiconductor element and the electrode pattern, and a metal substrate on which the laminated substrate is mounted. In the device
The electrode pattern is a metal joint body obtained by joining a first metal portion and a second metal portion, and is viewed from above in both the vertical direction and the horizontal direction of the interface between the first metal portion and the second metal portion. A semiconductor device characterized in that regular gaps are lined up and the ratio of the gaps at the interface is 50% or less. The first step of forming an uneven shape on one surface of the second metal part, and
The surface of the second metal portion on which the concave-convex shape is formed and one surface of the first metal portion having a waviness are opposed to each other, and the convex portion of the concave-convex shape is plastically deformed by heating and pressurizing. Then, in the second step of joining the first metal part and the second metal part,
A method for producing a metal joint, which comprises. After the first step, before the second step,
The step of removing the oxide film of the first metal part and the second metal part using a reducing gas is performed.
The method for producing a metal joint according to claim 6, further comprising. The first step of forming an uneven shape on both sides of the intermediate metal part,
One surface of the first metal portion and one surface of the intermediate metal portion are opposed to each other, one surface of the second metal portion and the other surface of the intermediate metal portion are opposed to each other, and the heating and pressurizing are performed. A second step of joining the first metal portion and the intermediate metal portion, and the second metal portion and the intermediate metal portion by plastically deforming the convex portion of the concave-convex shape.
A method for producing a metal joint, which comprises. After the first step, before the second step,
The step of removing the oxide film of the first metal portion, the second metal portion, and the intermediate metal portion using a reducing gas is performed.
The method for producing a metal joint according to claim 8, further comprising. The method for producing a metal conjugate according to claim 7 or 9, wherein the reducing gas contains formic acid or hydrogen. The method for producing a metal joint according to any one of claims 6 to 10, wherein the height of the convex portion of the concave-convex shape is within the range of 0.1 to 20 μm. The method for producing a metal joint according to any one of claims 6 to 11, wherein the width of the convex portion of the concave-convex shape is in the range of 1 to 200 μm. The method for producing a metal joint according to any one of claims 6 to 12, wherein the distance between the convex portions of the concave-convex shape is in the range of 1 to 200 μm. The metal according to any one of claims 6 to 13, wherein the ratio of the width of the convex portions of the concave-convex shape to the distance between the convex portions of the concave-convex shape is in the range of 0.5 to 4. Method of manufacturing a joint. The method for producing a metal joint according to claim 6, wherein the height difference of the waviness is in the range of 0.5 μm to 10 μm. The first step of forming an uneven shape on one surface of the second metal part, and
The surface of the second metal portion on which the concave-convex shape is formed and the surface of the first metal portion provided on the laminated substrate in which waviness exists are opposed to each other, and the concave-convex shape is formed by heating and pressurizing. A second step of forming an electrode pattern by joining the first metal portion and the second metal portion by plastically deforming the convex portion.
The third step of mounting the semiconductor element on the laminated substrate and
The fourth step of assembling the laminated substrate into a laminated assembly, and
A fifth step of electrically connecting the semiconductor element and the electrode pattern on the laminated substrate, and
The sixth step of combining the resin case with the laminated assembly and
A method for manufacturing a semiconductor device, which comprises.

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